This invention relates generally to the construction of insulated refrigeration cabinets, and more particularly to cabinets used for chest-type food freezers having a generally open top covered by a horizontally hinged and upward opening door.
Chest-type food freezers comprise essentially a rectangular box construction comprising an insulated wall in which the insulation is usually a polyurethane foam. The outside of the box is a metallic outer shell, while within the box is a liner that is also generally made of metal, thus forming a box within a box with the space between being filled with foam insulation. By the use of a rigid polyurethane foam, considerable structural strength can be obtained by using relatively thin metal for both the outer shell and the inner liner. Around the open upper end of the box, a plastic thermal breaker strip is usually fitted over the insulation space to bridge the space between the shell and the liner and to provide a smooth finished surface. An insulated lid or door is hinged at the back and generally carries a deformable elastomeric gasket to make sealing contact with the breaker strip to minimize heat transfer between the inside and outside of the freezer.
In the case of chest-type food freezers, it has long been common practice not to use separate exposed evaporator and condenser elements for the refrigeration system, but rather to attach the coils of tubing directly to the respective metal liner and shell surfaces for most efficient heat transfer. Thus, the condenser takes the form of serpentine coils that are fastened to the inner surface of the outer shell, and the evaporator takes the form of similar coils which are secured to the outer surface of the inner liner, so that the shell and liner become the effective heat transfer surfaces for the appliance. The remaining portion of the refrigeration system is the compressor, which is usually housed in a compartment recessed into one end or a rear corner of the liner, which results in a step on the inside of the liner to accommodate the compressor compartment. The outer shell is then formed with suitable reinforcing in the area of the compressor compartment, as well as openings to allow air circulation for cooling. Thus, the outer shell in the area of the compressor compartment must be generally made heavier, since it is not stiffened by the foam insulation, and likewise a special insert must be placed to form the inner wall of the compressor compartment and to provide the outer surface for the foamed insulation area in the area of the stepped portion of the liner.
Chest-type food freezers are generally built in a number of different sizes, ranging from perhaps 10 through 25 cubic feet in capacity, and for ease of fabrication, such chests are often made with a fixed vertical height and depth, and thereby vary only in the length of the cabinet to determine the total capacity of the unit. With this type of construction, the larger units, which require more refrigeration capacity, necessarily have longer tubing lengths for the condenser and evaporator because of the longer front and back wall lengths of the larger size cabinets. Generally, such cabinets have been made from coils of sheet steel, with all four side walls of the shell and the liner each being formed from a single piece which is blanked and notched as required to form the upper and lower edges. After the blanking is completed, a preformed serpentine coil is laid on the appropriate surface and fastened in place by suitable means, such as welded straps, so that the tubing will remain in place as the sides, including the tubing, are bent into a rectangular shape and the ends secured together by a suitable means, such as welding. After this is done, the bottom pieces are welded in place and other parts, such as hinged tapping plates and the compressor mounting structure, are secured to the respective members, after which they are painted to provide the desired finish. When the shell and liner are complete, the liner is inserted in the shell and positioned by suitable means, such as insulating blocks, for the foaming operation, and suitable vent strips and spacers placed adjacent the upper end to close off the gap between the shell and liner, after which the foaming operation is performed. The finished cabinet is then ready for the application of the breaker strips, the attachment of the top, and the mounting of the compressor and the remaining portions of the assembly operation.
The foregoing procedure is a rather time-consuming and labor-intensive operation. One of the steps which is required before the liner and the shell are finally assembled is to apply a thermal mastic to the coil serpentines to ensure proper thermal conductivity between the tubing and the surface of the liner and shell. The thermal mastic material is generally applied by hand to both the shell and liner just before the liner is inserted into the shell in a time-consuming operation which requires high skill and a certain amount of wastage of the thermal mastic material as a result of excess application to get the required coverage.
Another problem is that the painting operations also require a high degree of skilled labor and expensive equipment associated with paint spray operations.
It has been recognized that the attachment of the coils in the shell and liner can be done with a much reduced labor requirement if methods other than welding straps can be used to attach the coils to the shell and liner. Furthermore, it is possible to eliminate the painting operation if prepainted sheets can be used if they can be fabricated without any welding which would ruin the prepainted surface. Furthermore, the use of methods other than welding permits the use of other materials such as aluminum and galvanized steel, which would make welding operations excessively difficult.
One such approach is to use an adhesive applied by dipping the liner, with the attached coils, into a vat of suitable adhesive. This arrangement has been shown by U.S. Pat. Nos. 3,799,831; 3,907,267; and 3,912,005, in the name of L. N. Griffiths. Another approach has been to hold the coils in place by a suitable clamping means and then use a spray of high-density polyurethane foam having sufficient structural strength to hold the coils in place, as shown in U.S. Pat. Nos. 3,904,721 and 3,966,283, in the name of R. L. Puterbaugh. Other approaches to the use of prepaint material are shown in U.S. Pat. Nos. 3,948,407 and 4,082,825, both in the name of R. L. Puterbaugh. However, these approaches still require excessive labor and material, and do not lend themselves to a fully automated type of assembly, which is required to reduce the labor content, and hence the costs, of the finished appliance.